1. Field of the Invention
The present invention generally relates to an optical writing system and an image forming apparatus, and, in particular, to an optical writing system directed to miniaturization thereof, and an image forming apparatus employing the thus-miniaturized optical writing system.
Further, the present invention relates to an image forming apparatus, such as a copying machine, a printer, a facsimile, or a plotter, which includes an optical writing device which applies an optical beam on to-be-scanned surfaces of a plurality of image carrying bodies disposed in parallel, and thus writes latent images thereon, respectively. The image forming apparatus then forms a multi-color image using the thus-formed respective latent images.
2. Description of the Related Art
In the related art, for example, four image carrying bodies (for example, photosensitive drums) installed to be exposed by optical beams emitted from a plurality of light sources. Thereby, latent images are written on the respective image carrying bodies. Then, these latent images are developed by developers of different colors (for example, toners of yellow, magenta, cyan and black). After the development and thus, visible images (toner images) are formed, these images are transferred onto a transfer medium, such as a record paper supported by a transfer conveyance belt etc, from the respective image carrying bodies, one by one, at respective transfer parts thereof. After laying the visible image of each color formed on each image carrying body on top of each other, onto the transfer medium and thus transferring it thereonto in a superimposing manner, the thus-formed multi-color image on the transfer medium is fixed thereonto, and, thus, a multi-color printed image is obtained. Such an image forming apparatus will be referred to as a tandem color image forming apparatus.
Although, in such a tandem color image forming apparatus, in some case, an optical writing device is provided separately for each image carrying body onto which a latent image is written individually. However, an optical writing device using an optical deflector which includes a polygon mirror and its motor for a drive is comparatively expensive, and to provide an optical writing device individually for every image carrying body has a problem in respect of costs of respective parts/components and/or manufacture costs of the entire image forming apparatus. Moreover, since an installation space required should be large in order to install a plurality of optical writing devices each having an optical deflector corresponding to the number of image carrying bodies, there is also a problem in that the entire image forming apparatus becomes large-sized.
Then, in order to attain effective reduction in the cost of such a tandem color image forming apparatus, and miniaturization thereof, an optical writing device has an optical deflector receiving optical beams applied by a plurality of light sources, carries out deflection of the optical beams applied by the plurality of light sources and thereby scanning a plurality of image carrying bodies. Thus, the single optical deflector simultaneously performs optical writing onto the plurality of image carrying bodies.
In the optical writing device which carries out deflection and scanning by the optical beams from the plurality of light sources with one optical deflector simultaneously on the plurality of image carrying bodies, and performs optical writing, an optical system which directs a plurality of optical beams and form images onto the respective image carrying bodies are arranged symmetrically in two directions with respect to the optical deflector. However, since the optical system includes a large number of optical components corresponding to the plurality of optical beams, miniaturization of the optical writing device would be difficult.
The present invention has been devised in consideration of the above-mentioned situation, and, an object of the present invention is to provide an image forming apparatus including an optical writing device, wherein a configuration/structure of a housing of the optical writing device and a configuration/arrangement of optical system are such as that enabling further miniaturization of the optical writing device.
An optical writing device according to the present invention includes:
a plurality of light sources;
an optical deflector deflecting optical beams generated by the plurality of light sources in two symmetrical directions;
optical systems disposed in the two symmetrical directions with respect to the optical deflector, and directing the optical beams deflected by the optical deflector into respective surfaces to be scanned, and forming images thereon; and
a housing containing the plurality of light sources, optical deflector and optical systems,
wherein:
the housing comprises a base plate on which the optical deflector and optical system are disposed, and a side wall part surrounding the base plate;
the base plate divides the housing into two sections;
the plurality of light sources are disposed on the side wall part;
the optical deflector is disposed approximately at the center of said base plate; and
optical components of the optical systems are distributed into the two sections of the housing.
Thus, the optical writing device includes the plurality of light sources, the optical deflector which distributes the optical beams from these light sources and deflects them in the symmetrical two directions, the optical systems arranged symmetrically corresponding to the above-mentioned two directions with respect to the optical deflector and direct the thus-deflected four optical beams onto the respective to-be-scanned surfaces. Further, in the optical writing device, the plurality of light sources, optical deflector, and optical systems are arranged in the single housing. Further, in this optical writing device, the housing includes the base plate on which the above-mentioned optical deflector and optical systems are arranged, and the side wall part having the shape of the frame surrounding the circumference of this base plate. The above-mentioned base plate is provided in the approximately central portion of the above-mentioned side wall part, and divides the housing vertically. Further, the above-mentioned light sources are provided on the side wall part of the above-mentioned housing, the above-mentioned optical deflector is disposed in the approximately central part of the above-mentioned base plate, the optical components of the optical systems are distributed on the top and bottom sides of the base plate. Thereby, the miniaturization of the optical writing device can be attained with securing the necessary light path length of the whole optical system.
An optical writing device according to another aspect includes:
a light source unit;
an optical deflector deflecting a optical beam generated by the source unit;
an optical system directing the optical beam deflected by the optical deflector into a surface to be scanned, and forming an image thereon; and
a housing containing the light source unit, optical deflector and optical system,
wherein:
the housing comprises a base plate on which the optical deflector and optical system, and a side wall part surrounding the base plate;
the base plate divides the housing into two sections;
the light source unit is disposed on the side wall part; and
optical components of the optical system are distributed into the two sections of the housing.
The housing may be such that the base plate and side wall part are formed by integral resin molding; and
the housing has an approximately H-shaped sectional view.
Thus, since the above-mentioned housing including the base plate and side wall part is made by resin integral molding, and has the H-shaped sectional view, while miniaturization of the housing can be achieved, the strength thereof can be secured, and vibration by rotation of the optical deflector etc. can be effectively controlled, and the optical characteristic/performance thereof can be maintained. Moreover, since the housing is made of resin formed by molding, the weight can be made small, any post-processing is thus unnecessary, thereby productivity is high, and the manufacture cost can be held down.
The housing may be formed of a resin material having an expansivity smaller than that of a frame of an image forming apparatus body to which the optical writing device is mounted.
Thus, since the expansivity of the frame of the image forming apparatus body to which the housing of the optical writing device is mounted and the expansivity of the housing are close although the housing is made of resin, distortion of the housing of the optical writing device due to temperature change etc. is not likely to occur, and thus the above-mentioned housing can maintain the optical characteristic of the optical writing device, in the state in which the housing of the optical writing device is fixed to the frame of the image formation apparatus body.
An image forming apparatus according to the present invention includes:
a plurality of image carrying bodies disposed side by side;
the above-described optical writing device writing latent images onto the plurality of image carrying bodies by applying the optical beams thereto, respectively;
a developing unit developing the latent images formed on the plurality of image carrying bodies and visualizes them; and
a transfer unit carrying transfer material at positions of the respective image carrying bodies, and transferring the thus-visualized images of respective color components onto the transfer material from the respective image carrying bodies, one by one.
Thus, the plurality of image carrying bodies, the optical writing device which apples the optical beams and writes latent images on the respective to-be-scanned surfaces of the image carrying bodies, the development unit developing and forming visible images from the latent images formed on the respective image carrying bodies by developers of respective different color components, a unit which conveys transfer material (paper) and lays the visible images of respective color components onto the conveyed transfer material (paper) one by one at the positions of the respective image carrying bodies on top of each other, and thus transfers them, and a unit which fixes the thus-formed multi-color image formed on the transfer material (paper) thereto. In this configuration, since the above-described compact-sized optical writing device is employed, it is possible to provide a miniaturized, inexpensive, tandem full-color image forming apparatus.
Such an optical writing device as that described above may include an optical system including an optical scanning lens which comprises:
a lens part converging the deflected beam, deflected in a predetermined range, onto the surface to be scanned;
a reinforcement part reinforcing the lens part; and
at least one standing wall projecting from either one of both ends along the longitudinal direction of the lens part in a beam exit direction,
wherein the lens part, reinforcement part and at least one standing wall are formed integrally; and
an angle xcex82 of an inner surface of the at least one standing wall with respect to an optical axis of the lens part is larger than an angle xcex81 of the deflected beam at the end of the lens part and the optical axis of the lens part.
Thereby, distortion and deformation of the lens part can be avoided by the integrally formed reinforcement part, the deflected beam passing through the end part of the lens part can be prevented from being reflected by the standing wall, and, thus, the end part of the effective scanning range can be prevented from being abnormally high in luminous energy, and, thus, generation of abnormality in a resulting printed image can be effectively prevented.
Such an optical writing device as that described above may instead include an optical system including an optical scanning lens which comprises:
a lens part converging the deflected beam, deflected in a predetermined range, onto the surface to be scanned;
a reinforcement part reinforcing the lens part; and
at least one standing wall projecting from either one of both ends along the longitudinal direction of the lens part in a beam exit direction,
wherein the lens part, reinforcement part and at least one standing wall are formed integrally; and
an inner surface of the at least one standing wall is inclined with respect to a plane perpendicular to a deflection plane formed by the deflected beam incident on the lens part being deflected by the optical deflector.
Thereby, distortion and deformation of the lens part can be avoided by the integrally formed reinforcement part, the deflected beam passing through the end part of the lens part and even being reflected by the standing wall can be caused to be directed apart from the deflection plane, and, thus, the end part of the effective scanning range can be prevented from being abnormally high in luminous energy, and, thus, generation of abnormality in a resulting printed image can be effectively prevented.
An incident surface of the lens part may include a concave surface including a toroidal surface. In this configuration, the toroidal lens can be prevented from being distorted or deformed, by the reinforcement part, and, also, the problems occurring due to reflection of the deflected beam by the standing wall can be avoided as described above for the toroidal lens.
An image forming apparatus according to another aspect of the present invention includes:
the above-described optical scanning lens, disposed so as to face a surface to be scanned; and
an optical deflector deflecting a laser beam so as to cause it to scan the surface to be scanned through the optical scanning lens.
Thereby, in the image forming apparatus, the optical scanning lens can be prevented from being distorted or deformed, by the reinforcement part, and, also, the problems occurring due to reflection of the deflected beam by the standing wall of the optical scanning lens can be avoided as described above.